1. Field of the Invention
The present invention relates to a cutting blade for a mowing apparatus driven by an engine or the like to mow grass or sprig or the like, and in particular to a cutting blade of a mowing apparatus which comprises a pair of cutting wheels slidably superposed with each other and oscillatingly and reciprocatingly rotating in mutually opposite directions through a predetermined angle, respectively, and each provided with a number of grass cutting teeth ,along its circumference at substantially equal intervals, whereby cutting the grass in shear mode as by scissors.
2. Description of the Prior Art
Conventionally, as a cutting blade for a mowing machine for mowing grass or sprig, a single rotatable cutter wheel which is supported by a cutter support body and is driven by an engine or a motor via a drive shaft passed through a hollow pipe connected between the engine and the cutter support body was used. Therefore, when the worker grips two grip portions by both hands and swings the hollow pipe to and fro, it is possible to mow grass by the single rotating cutter wheel.
Specifically, as shown in FIG. 1, the conventional mowing apparatus includes a rotary cutting wheel CW having a number of cutting edges CE at the outer periphery thereof. The rotary cutting wheel CW is rotatably supported by a bearing casing BC (cutter support body) and further driven by an engine EN via a transmission shaft rotatably passed through a hollow pipe HP connected between the bearing casing BC and the engine EN. A handle HA including a first grip G.sub.1 is fixed at roughly the middle of the hollow pipe HP, and a second grip G.sub.2 is directly fitted onto the hollow pipe HP so that the worker can swing the cutting wheel to and fro by griping the grips G1 and G2 by both hands.
In more detail with reference to FIG. 2, the transmission shaft TS driven by the engine EN is rotatably supported by two bearings BE provided on a junction point between the bearing casing BC and the hollow pipe HP. At the lowermost end of the transmission shaft TS, a first bevel gear BG.sub.1 is fixed. On the other hand, a wheel shaft WS is also rotatably supported by two bearings BE fixed to the lower side of the bearing casing BC. At the uppermost end of the wheel shaft WS, a second bevel gear BG.sub.2 is formed so as to be in mesh with the first bevel gear BG.sub.1. The cutting wheel CW is pinched between two washers WA.sub.1 and WA.sub.2 and fixed to the wheel shaft WS with a spline SP and a nut N.
When the worker grips the two grips G.sub.1 and G.sub.2 and swings the hollow pipe HP to and fro, grass can be mowed by the cutting wheel CW driven by the engine EN at a relatively high speed.
In the conventional mowing machine, however, since only the single cutter wheel rotates at a relatively high speed, there exist various problems such that pebblestones may be dangerously kicked off; the machine itself must be swung violently to mow grass; and soft grass usually remains unmowed.
In order to overcome the problems in the conventional mowing machine as set forth above, there were proposed some improved mowing apparatus having a cutting blade comprising two superposed cutting wheels, which are for example disclosed in U.S. Pat. No. 3,631,658, U.S. Pat. No. 3,472,007 or EP Al No. 0 257 566 or the like.
The improved mowing apparatus were very convenient since grass could be cut in shearing mode as by a scissors. However, unfortunately, in the cutting blades of the improved mowing apparatuses, there was another problem. Namely, in the cutting blades, each of the teeth of the cutting blade has an acute angle or the outer periphery edge of each teeth has a cutting edge. This means that dangerousness would be increased when the apparatus is used, since the tip portions of the teeth or the outer peripheries of the teeth are is likely to contact with the worker or the like during the operation thereof, thus leading injury of the worker. Further, there is a possibility that grass unnecessary to be cut may be cut by the cutting edge provided on the outer periphery of the tooth. Furthermore, if the cutting edge of the outer periphery of the tooth is inadvertently brought into contact with a hard object, such as a stone, rock or tree, the cutting edge may be damaged due to its fragile structure, thus impairing the cutting ability of the cutting wheels.
However, it should be noted that in the mowing apparatus having such a blade structure with two superposed cutting wheels which are oscillatingly and reciprocatingly rotated, it is not necessary to provide a cutting edge at the outer periphery of the tooth or to form the tip portion of the tooth acutely, since grass is cut by cutting edges provided on both side edges of each tooth in such a manner as a scissors.